tools/accounting: handle truncated taskstats netlink messages

tools/accounting: handle truncated taskstats netlink messages

procacct and getdelays use a fixed receive buffer for taskstats generic
netlink messages.  A multi-threaded process exit can emit a single
PID+TGID notification large enough to exceed that buffer on newer kernels.

Switch to recvmsg() so MSG_TRUNC is detected explicitly, increase the
message buffer size, and report truncated datagrams clearly instead of
misparsing them as fatal netlink errors.

Also print the taskstats version in debug output to make version
mismatches easier to diagnose while inspecting taskstats traffic.

Link: https://lkml.kernel.org/r/520308bb4cbbaf8dc2c7296b5f60f11e12fb30a5.1774810498.git.cyyzero16@gmail.com
Signed-off-by: Yiyang Chen <cyyzero16@gmail.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Dr. Thomas Orgis <thomas.orgis@uni-hamburg.de>
Cc: Fan Yu <fan.yu9@zte.com.cn>
Cc: Wang Yaxin <wang.yaxin@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>